The invention relates to an apparatus in the form of a tool comprising a flow channel.
No method has been known so far in which to change the width of the melt strand during extraction by modification of the geometry of the flow channel in the tool.
Various types of apparatuses as described above have been known. They are used especially in the field of plastics processing in flow channels for thermoplastic melts for the possibility of modification of flow channel resistance. EP 0 367 022, DE 35 30 383 A1, DE 44 00 069 C1 and DE-AS 12 1 412 teach extrusion dies in which to change the flow channel height. These known solutions comprise a more or less thick, solid, one-piece metal wall which can be deformed by adjusters pressing on the wall from the rear. They work only as long as the solid wall, during deformation, does not exceed the range of linear elasticity because they depend on the fact that upon return motion of the adjusters, the wall will take precisely its original initial position. Because of the comparatively thick wall required in these apparatuses for reasons of solidity, the possibilities of uniform adjustment of the wall over the entire width of the flow channel (overall adjustment) are restricted as well as the locally defined adjustment of a small portion of the wall (relative adjustment).
DE-OS 23 05 877 describes a limitation of a flow channel which consists of several thin individual sheets lying one upon the other over their full surfaces and consequently possesses higher flexibility. But this flexibility is purchased by this solution abandoning the important criterion of absolute leak-tightness towards the fluid flowing in the flow channel, because mobility of all the individual sheets in the marginal areas is required for adjustment. To this end, the marginal areas of the sheets reach into grooves which are located between the two halves of the flow channel body. The surface pressure necessary for leak-tightness in these marginal areas cannot be applied, because it would not allow any motion of the sheets relative to the flow channel halves.
Consequently, solutions offering a wide adjusting range accompanied with absolute leak-tightness of the flow channel have not been disclosed in the known apparatuses of the generic type. The known apparatuses neither offer the possibility to put a method into practice in which a melt strand is forced through an absolutely leak-tight tool channel, two independent adjusting systems, which are integrated in the tool and act on a wall of the flow channel, serving to modify the thickness of the melt strand during melt discharge either in its entirety or only locally at certain places or to change both simultaneously, nor to change the width of the melt strand during extraction by changing the geometry of the flow channel in the tool.
The invention relates to a flow channel with a width or circumference-to-height ratio greater than 10, and a mechanism for the absolutely leak-tight limitation of a flat flow channel. The mechanism insures that, by means of externally accessible adjusters, at least one flow channel wall can be adjusted in its overall position to the largest extent possible, i.e., uniformly over the entire width, as well as locally, i.e., in strictly defined portions over the width, in relation to the opposite demarcation of the flow channel.
The invention further relates to a method, using another embodiment of the invention, for continuously discharging a melt strand by means of a tool having at least one adjustable wall, in which, during the discharge of the melt, the height of the entire flow channel is adjusted by a first adjusting system and portions of the flow channel are adjusted by a second adjusting system independent of the first adjusting system and using a second control system. With this method, during the discharge the thickness of the melt strand changes entirely, or only locally at certain places, or both changes take place simultaneously.
It is the object of the invention to embody an apparatus of the generic type in such a way that increased ranges of overall and relative adjustment are possible, accompanied with simultaneous absolute leak-tightness of the apparatus, and based on this to develop methods by which, during extraction, a melt strand can be modified in thickness entirely or locally as well as in width.
According to the invention, this object is attained in that adjusters act from behind on a flexible flow channel wall which is produced by individual sheets being placed one upon the other over their full surfaces, the individual sheet that the fluid flows along being a flow channel sheet which cooperates with the flow channel to form a wall and is firmly welded into the flow channel body all around.
The method of discharging a melt strand is put into practice in that during the production of the melt strand by means of a tool, the height of the outlet gap of the tool is modified over the entire width or only locally during the melt extraction by means of two independent adjusters which act on at least one of the two outlet lips so that during the time of extraction, the melt strand can be modified in thickness entirely or locally as well as in width.
The term sheet stack means a stack of sheets, the undersides of each of which resting tightly on the top sides of the sheet underneath. In one embodiment, a sheet, one surface of which forms a flow channel wall, can also be integrated in a frame which is integrated in the flow channel by screwing, welding or in a similarly leak-tight way. In another embodiment, the desired flexibility of the sheet stack is obtained by the individual sheets having a thickness of less than 2 mm, preferably less than 1 mm. In one embodiment, it can be functional for the apparatus that at least one of the edges of the individual sheets is welded together with a frame or the body into which the flow channel is integrated. As regards the flexibility of the sheet stack, the present invention provides by special advantage that the stack to has a curvature instead of being plane. The invention also provides another extension of the adjusting range is attained by the adjusters being bonded to the sheet stack non-positively so that the latter can be deformed by traction and pressure.
The invention provides a special provides a special advantage by using two independent adjusters acting on a flexible wall of the apparatus, it being possible, by the aid of the first adjusters, to effect uniform adjustment of the wall over the entire width and additionally, by the aid of the second adjusters, to deform the wall locally over the width. Maximum adjustment is attained if, two independent adjusters act on two walls of the flow channel, it being possible to effect a uniform adjustment of the respective wall over the entire width by means of the first adjusters and additionally to deform the respective wall locally defined over the width by means of the second adjusters. The non-positive integration once again enlarges the adjusting range, because thus the wall cannot only be pressed into the flow channel, but can also be retracted.